Magnetic sensor and an integrated circuit

ABSTRACT

The present teaching relates to a magnetic sensor comprising an input port, a magnetic field detecting circuit that generates a magnet detection signal, an output control circuit that controls operation of the magnetic sensor, and an output port. The magnetic field detecting circuit includes a magnetic sensing element that detects an external magnetic field and output a detection signal, a signal processing element configured to amplify the detection signal and removing interference from the detection signal, and an analog-digital conversion element configured to convert the processed detection signal into a magnet detection signal, and the output control circuit controls the magnetic sensor to operate in at least one of a first state and a second state responsive to at least the magnet detection signal, wherein the signal processing element comprises a folded cascode amplifier.

CROSS REFERENCE TO RELATED APPLICATIONS

This non-provisional patent application is a continuation-in-part ofU.S. patent application Ser. No. 14/822,353, which claims priority toChinese Patent Application No. 201410390592.2, filed on Aug. 8, 2014 andto Chinese Patent Application No. 201410404474.2, filed on Aug. 15,2014. In addition, this non-provisional patent application claimspriority under the Paris Convention to PCT Patent Application No.PCT/CN2015/086422, filed with the Chinese Patent Office on Aug. 7, 2015,to Chinese Patent Application No. CN201610203609.8, filed with theChinese Patent Office on Apr. 1, 2016, and to Chinese Patent ApplicationNo. CN201610387820.X, filed with the Chinese Patent Office on Jun. 2,2016 all of which are incorporated herein by reference in theirentirety.

BACKGROUND

1. Technical Field

The present teaching relates to a field of circuit technology. Inparticular, the present teaching relates to a magnetic sensor. Thepresent teaching further relates to a driver for a permanent magneticmotor.

2. Discussion of Technical Background

During starting of a synchronous motor, the stator produces analternating magnetic field causing oscillation of a permanent magneticrotor. The amplitude of the oscillation of the rotor increases until therotor begins to rotate, and finally the rotor is accelerated to rotatein synchronism with the alternating magnetic field of the stator. Toensure the starting of a conventional synchronous motor, a startingpoint of the motor is set to be low, which results in that the motorcannot operate at a relatively high working point, thus the efficiencyis low. In addition, the rotor cannot be ensured to rotate in a samedirection every time as a stop or stationary position of the permanentmagnetic rotor is not fixed. Accordingly, in applications such as a fanand water pump, the impeller driven by the rotor has straight radialvanes, which results in a low operational efficiency of the fan andwater pump.

FIG. 1 illustrates a conventional drive circuit for a synchronous motor,which allows a rotor to rotate in a same predetermined direction everytime when it starts. In the circuit, a stator winding 1 of the motor isconnected in series with a TRIAC between two terminals M and N of an ACpower source VM, and an AC power source VM is converted by a conversioncircuit DC into a direct current voltage and the direct current issupplied to a position sensor H. A magnetic pole position of a rotor inthe motor is detected by the position sensor H, and an output signal Vhof the position sensor H is connected to a switch control circuit PC tocontrol the bidirectional thyristor T.

FIG. 2 illustrates waveforms at various locations of the drive circuit.It can be seen from FIG. 2 that, in the drive circuit, whether thebidirectional thyristor T is switched on or off, the AC power sourcesupplies power for the conversion circuit DC so that the conversioncircuit DC constantly outputs and supplies power for the position sensorH (referring to a signal VH in FIG. 2). In a low-power application, in acase that the AC power source provides commercial electricity of about200V, the electric energy consumed by two resistors R2 and R3 in theconversion circuit DC is more than the electric energy consumed by themotor.

The magnetic sensor applies Hall effect, in which, when current I runsthrough a substance and a magnetic field B is applied in a positiveangle with respect to the current I, a potential difference V isgenerated in a direction perpendicular to the direction of current I andthe direction of the magnetic field B. The magnetic sensor is oftenimplemented to detect the magnetic polarity of an electric rotor.

As the circuit design and signal processing technology advances, thereis a need to improve the magnetic sensor and the implemented IC for theease of use and accurate detection.

SUMMARY

The present teaching provides a magnetic sensor and application(s)thereof. According to an embodiment of the present teaching, A magneticsensor comprises an input port to be connected to an external powersupply; a magnetic field detecting circuit configured to generate amagnet detection signal; an output control circuit configured to controloperation of the magnetic sensor in response to the magnet detectionsignal; and an output port, wherein the magnetic field detecting circuitincludes: a magnetic sensing element configured to detect an externalmagnetic field and output a detection signal, a signal processingelement configured to amplify the detection signal and removinginterference from the detection signal to generate processed detectionsignal, and a conversion element configured to convert the processeddetection signal into the magnet detection signal, which is used tocontrol the magnetic sensor to operate in at least one of a first stateand a second state responsive to at least the magnet detection signal,wherein in the first state, a load current flows from the output port tooutside of the magnetic sensor, and in the second state, a load currentflows from the outside into the output port of the magnetic sensor,wherein the signal processing element comprises a folded cascodeamplifier.

In some embodiments, the detection signal includes a magnetic fieldsignal and a deviation signal, and the signal processing elementcomprises a first chopper switch configured to separate the detectionsignal into the deviation signal and the magnetic field signalcorresponding to a chopper frequency and a baseband frequency,respectively, a chopper amplifier configured to amplify the deviationsignal and the magnetic field signal and to switch the amplifieddeviation signal and the amplified magnetic field signal onto thechopper frequency and the baseband frequency, respectively, and a filtercircuit configured to filter out the deviation signal at the chopperfrequency.

In some embodiments, the chopper amplifier comprises a first amplifier;and a second chopper switch, wherein the first amplifier includes thefolded cascode amplifier that is configured to perform first-stageamplification on the deviation signal and the magnetic field signal fromthe first chopper switch to generate the amplified deviation signal andthe amplified magnetic field signal, respectively, and the secondchopper switch is configured to switch the amplified deviation signaland the amplified magnetic field signal onto the chopper frequency andthe baseband frequency, respectively.

In some embodiments, the chopper frequency is greater than 100 K Hertzand the baseband frequency is less than 200 Hertz.

In some embodiments, the chopper amplifier further comprises a secondamplifier connected in serial to the second chopper switch, wherein thesecond amplifier is configured to perform second-stage amplification onthe amplified deviation signal switched onto the chopper frequency andthe amplified magnetic field signal switched onto the basebandfrequency.

In some embodiments, the signal processing element further comprises asample-and-hold circuit coupled between the chopper amplifier and thefilter circuit, wherein the sample-and-hold circuit is configured tosample a first pair of differential signals during a first half and asecond half of a clock cycle, respectively and output two pairs ofsampled differential signals during the clock cycle.

In some embodiments, the filter circuit further comprises a first filterconfigured to compute a second pair of differential signals based on thetwo pairs of sampled differential signals.

In some embodiments, the filter circuit further comprises a secondfilter configured to further amplify the second pair of differentialsignals, remove the deviation signal, and generate a third pair ofdifferential signals.

In some embodiments, the magnetic sensor further comprises a rectifyingcircuit coupled with the input port and configured to provide a voltagesupply to the magnetic field detection circuit.

In some embodiments, the external power supply is an alternating current(AC) power supply, and the magnet detection signal is a switchingdetection signal, wherein a switching frequency of the magneticdetection signal is proportional to a frequency of the AC power supplyor is twice the frequency of the AC power supply.

In some embodiments, the magnetic sensor further comprises an outputcontrol circuit configured to control the magnetic sensor to operate inat least one of the first state and the second state based on the magnetdetection signal, wherein the output control circuit comprises a firstswitch coupled with the output port to form a first current pathallowing the load current flows from the output port to outside of themagnetic sensor in the first state; and a second switch coupled with theoutput port to form a second current path allowing the load currentflows from outside of the magnetic sensor to the output port in thesecond state, wherein the first and second switches operate based on themagnet detection signal to selectively turn on the first and secondcurrent paths.

In some embodiments, the first switch is a diode and the second switchis either a diode or a transistor.

According to another embodiment of the present teaching, an integratedcircuit for a magnetic sensor comprises an input port to be connected toan external power supply; an output port; and a magnetic field detectingcircuit configured to generate a magnet detection signal and comprises amagnetic sensing element configured to detect an external magnetic fieldand output a detection signal, wherein the detection signal includes amagnetic field signal and a deviation signal, a signal processingelement configured to amplify the detection signal and removeinterference to generate a processed detection signal, and a conversionelement configured to convert the processed detection signal to themagnet detection signal, which is used to control the magnetic sensor tooperate in at least one of a first state and a second state responsiveto at least the magnet detection signal, wherein the signal processingelement comprises a first chopper switch configured to separate thedetection signal into a magnetic field signal and a deviation signalcorresponding to a chopper frequency and a baseband frequency,respectively; a chopper amplifier configured to separately amplify themagnetic field signal and the deviation signal and switch the amplifieddeviation signal and the amplified magnetic field signal onto thechopper frequency and the baseband frequency, respectively, and a filtercircuit configured to remove the deviation signal that has been switchedto the chopper frequency, wherein the signal processing elementcomprises a folded cascode amplifier.

According to another embodiment of the present teaching, a motorassembly comprises a motor coupled with an external power supply thatprovides alternating current (AC) power to the motor; a magnetic sensorconfigured to detect a magnetic field generated by the motor; and abidirectional switch configured to control the motor based on anoperating state of the magnetic sensor determined based on the detectedmagnetic field, wherein the magnetic sensor comprises a magnetic fielddetecting circuit configured to detect the magnetic field and generate amagnet detection signal based on the detected magnetic field, andcomprises a magnetic sensing element configured to detect an externalmagnetic field and output a detection signal, a signal processingelement configured to amplify the detection signal and removinginterference from the detection signal to generate processed detectionsignal, and a conversion element configured to convert the processeddetection signal into the magnet detection signal, which is used tocontrol the magnetic sensor to operate in at least one of a first stateand a second state responsive to at least the magnet detection signal;and an output control circuit configured to control, based on the magnetdetection signal, the magnetic sensor to operate in at least one of afirst state and a second state responsive to at least the magnetdetection signal, wherein in the first state, current flows from outsideof the magnetic sensor into the magnetic sensor, and in the secondstate, the current flows from the magnetic sensor to the outside of themagnetic sensor, wherein the signal processing element comprises afolded cascode amplifier.

BRIEF DESCRIPTION OF THE DRAWINGS

The methods, systems, and/or programming described herein are furtherdescribed in terms of exemplary embodiments. These exemplary embodimentsare described in detail with reference to the drawings. Theseembodiments are non-limiting exemplary embodiments, in which likereference numerals represent similar structures throughout the severalviews of the drawings, and wherein:

FIG. 1 illustrates a prior art drive circuit for a synchronous motor,according to an embodiment of the present teaching;

FIG. 2 illustrates waveforms at various locations of the drive circuitshown in FIG. 1;

FIG. 3 illustrates a representation of a synchronous motor, according toan embodiment of the present teaching;

FIG. 4 illustrates a block diagram of a drive circuit for a synchronousmotor, according to an embodiment of the present teaching;

FIG. 5 illustrates a drive circuit for a synchronous motor, according toan embodiment of the present teaching;

FIG. 6 illustrates waveforms at different locations of the drive circuitshown in FIG. 5;

FIGS. 7 to 10 illustrate different embodiments of a drive circuit of asynchronous motor, according to an embodiment of the present teaching;

FIG. 11 illustrates an exemplary schematic diagram of a magnetic sensor,according to an embodiment of the present teaching;

FIG. 12 illustrates an exemplary schematic diagram of the signalprocessing element 1110, according to an embodiment of the presentteaching;

FIG. 13A illustrates an exemplary schematic diagram of a chopperamplifier 1204, according to an embodiment of the present teaching;

FIG. 13B illustrates an exemplary schematic diagram of a chopperamplifier 1204, according to another embodiment of the present teaching;

FIG. 14 illustrates an exemplary schematic diagram of a magnetic sensor,according to an embodiment of the present teaching;

FIG. 15 illustrates an exemplary schematic diagram of a rectifiercircuit 1402, according to an embodiment of the present teaching;

FIG. 16 illustrates an exemplary circuit diagram of a Hall detector 1420and the first chopper switch, according to an embodiment of the presentteaching;

FIG. 17 illustrates exemplary signal outputs, according to the circuitdiagram of FIG. 16;

FIG. 18 illustrates an exemplary circuit diagram of filter circuit 1428,according to an embodiment of the present teaching;

FIG. 19 illustrates an exemplary circuit diagram of comparator circuit1430, according to an embodiment of the present teaching;

FIG. 20 illustrates an exemplary schematic diagram for determining thepolarity of the magnetic field;

FIG. 21 illustrates exemplary signal outputs in a clock cycle;

FIG. 22 illustrates an exemplary circuit diagram of the output controlcircuit 1406, according to an embodiment of the present teaching;

FIG. 23 illustrates an exemplary circuit diagram of the output controlcircuit, according to another embodiment of the present teaching;

FIG. 24 illustrates an exemplary circuit diagram of the output controlcircuit, according to yet another embodiment of the present teaching;

FIG. 25 illustrates an exemplary schematic diagram of an motor 2500which incorporates a magnetic sensor constructed in accordance with thepresent teaching; and

FIG. 26 illustrates an exemplary schematic diagram of a synchronousmotor 2600 which incorporates a magnetic sensor constructed inaccordance with the present teaching.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth by way of examples in order to provide a thorough understanding ofthe relevant teachings. However, it should be apparent to those skilledin the art that the present teachings may be practiced without suchdetails. In other instances, well known methods, procedures, systems,components, and/or circuitry have been described at a relativelyhigh-level, without detail, in order to avoid unnecessarily obscuringaspects of the present teachings.

Throughout the specification and claims, terms may have nuanced meaningssuggested or implied in context beyond an explicitly stated meaning.Likewise, the phrase “in one embodiment/example” as used herein does notnecessarily refer to the same embodiment and the phrase “in anotherembodiment/example” as used herein does not necessarily refer to adifferent embodiment. It is intended, for example, that claimed subjectmatter include combinations of example embodiments in whole or in part.

In general, terminology may be understood at least in part from usage incontext. For example, terms, such as “and”, “or”, or “and/or,” as usedherein may include a variety of meanings that may depend at least inpart upon the context in which such terms are used. Typically, “or” ifused to associate a list, such as A, B or C, is intended to mean A, B,and C, here used in the inclusive sense, as well as A, B or C, here usedin the exclusive sense. In addition, the term “one or more” as usedherein, depending at least in part upon context, may be used to describeany feature, structure, or characteristic in a singular sense or may beused to describe combinations of features, structures or characteristicsin a plural sense. Similarly, terms, such as “a,” “an,” or “the,” again,may be understood to convey a singular usage or to convey a pluralusage, depending at least in part upon context. In addition, the term“based on” may be understood as not necessarily intended to convey anexclusive set of factors and may, instead, allow for existence ofadditional factors not necessarily expressly described, again, dependingat least in part on context.

FIG. 3 schematically shows a synchronous motor according to anembodiment of the present invention. The synchronous motor 10 includes astator 12 and a permanent magnet rotor 14 rotatably disposed betweenmagnetic poles of the stator 12, and the stator 12 includes a statorcore 15 and a stator winding 16 wound on the stator core 15. The rotor14 includes at least one permanent magnet forming at least one pair ofpermanent magnetic poles with opposite polarities, and the rotor 14operates at a constant rotational speed of 60 f/p during a steady statephase in a case that the stator winding 16 is connected to an AC powersupply, where f is a frequency of the AC power supply and p is thenumber of pole pairs of the rotor.

Non-uniform gap 18 is formed between the magnetic poles of the stator 12and the permanent magnetic poles of the rotor 14 so that a polar axis Rof the rotor 14 has an angular offset a relative to a central axis S ofthe stator 12 in a case that the rotor is at rest. The rotor 14 may beconfigured to have a fixed starting direction (a clockwise direction inthis embodiment as shown by the arrow in FIG. 3) every time the statorwinding 16 is energized. The stator and the rotor each have two magneticpoles as shown in FIG. 3. It can be understood that, in otherembodiments, the stator and the rotor may also have more magnetic poles,such as 4 or 6 magnetic poles.

A position sensor 20 for detecting the angular position of the rotor isdisposed on the stator 12 or at a position near the rotor inside thestator, and the position sensor 20 has an angular offset relative to thecentral axis S of the stator. Preferably, this angular offset is also a,as in this embodiment. Preferably, the position sensor 20 is a Halleffect sensor.

FIG. 4 shows a block diagram of a drive circuit for a synchronous motoraccording to an embodiment of the present invention. In the drivecircuit 22, the stator winding 16 and the AC power supply 24 areconnected in series between two nodes A and B. Preferably, the AC powersupply 24 may be a commercial AC power supply with a fixed frequency,such as 50 Hz or 60 Hz, and a supply voltage may be, for example, 110V,220V or 230V. A controllable bidirectional AC switch 26 is connectedbetween the two nodes A and B, in parallel with the stator winding 16and the AC power supply 24. Preferably, the controllable bidirectionalAC switch 26 is a TRIAC, of which two anodes are connected to the twonodes A and B respectively. It can be understood that, the controllablebidirectional AC switch 26 alternatively may be two silicon controlrectifiers reversely connected in parallel, and control circuits may becorrespondingly configured to control the two silicon control rectifiersin a preset way. An AC-DC conversion circuit 28 is also connectedbetween the two nodes A and B. An AC voltage between the two nodes A andB is converted by the AC-DC conversion circuit 28 into a low voltage DC.The position sensor 20 may be powered by the low voltage DC output bythe AC-DC conversion circuit 28, for detecting the magnetic poleposition of the permanent magnet rotor 14 of the synchronous motor 10and outputting a corresponding signal. A switch control circuit 30 isconnected to the AC-DC conversion circuit 28, the position sensor 20 andthe controllable bidirectional AC switch 26, and is configured tocontrol the controllable bidirectional AC switch 26 to be switchedbetween a switch-on state and a switch-off state in a predetermined way,based on the magnetic pole position of the permanent magnet rotor whichis detected by the position sensor and polarity information of the ACpower supply 24 which may be obtained from the AC-DC conversion circuit28, such that the stator winding 16 urges the rotor 14 to rotate only inthe above-mentioned fixed starting direction during a starting phase ofthe motor. According to this embodiment of the present invention, in acase that the controllable bidirectional AC switch 26 is switched on,the two nodes A and B are shorted, the AC-DC conversion circuit 28 doesnot consume electric energy since there is no current flowing throughthe AC-DC conversion circuit 28, hence, the utilization efficiency ofelectric energy can be improved significantly.

FIG. 5 shows a circuit diagram of a drive circuit 40 for a synchronousmotor according to a first embodiment of the present disclosure. Thestator winding 16 of the synchronous motor is connected in series withthe AC power supply 24 between the two nodes A and B. A first anode T1of the TRIAC 26 is connected to the node A, and a second anode T2 of theTRIAC 26 is connected to the node B. The AC-DC conversion circuit 28 isconnected in parallel with the TRIAC 26 between the two nodes A and B.An AC voltage between the two nodes A and B is converted by the AC-DCconversion circuit 28 into a low voltage DC (preferably, low voltageranges from 3V to 18V). The AC-DC conversion circuit 28 includes a firstzener diode Z1 and a second zener diode Z2 which are reversely connectedin parallel between the two nodes A and B via a first resistor R1 and asecond resistor R2 respectively. A high voltage output terminal C of theAC-DC conversion circuit 28 is formed at a connection point of the firstresistor R1 and a cathode of the first zener diode Z1, and a low voltageoutput terminal D of the AC-DC conversion circuit 28 is formed at aconnection point of the second resistor R2 and an anode of the secondzener diode Z2. The voltage output terminal C is connected to a positivepower supply terminal of the position sensor 20, and the voltage outputterminal D is connected to a negative power supply terminal of theposition sensor 20. Three terminals of the switch control circuit 30 areconnected to the high voltage output terminal C of the AC-DC conversioncircuit 28, an output terminal H1 of the position sensor 20 and acontrol electrode G of the TRIAC 26 respectively. The switch controlcircuit 30 includes a third resistor R3, a fifth diode D5, and a fourthresistor R4 and a sixth diode D6 connected in series between the outputterminal H1 of the position sensor 20 and the control electrode G of thecontrollable bidirectional AC switch 26. An anode of the sixth diode D6is connected to the control electrode G of the controllablebidirectional AC switch 26. One terminal of the third resistor R3 isconnected to the high voltage output terminal C of the AC-DC conversioncircuit 28, and the other terminal of the third resistor R3 is connectedto an anode of the fifth diode D5. A cathode of the fifth diode D5 isconnected to the control electrode G of the controllable bidirectionalAC switch 26.

In conjunction with FIG. 6, an operational principle of the drivecircuit 40 is described. In FIG. 6, Vac indicates a waveform of voltageof the AC power supply 24, and lac indicates a waveform of currentflowing through the stator winding 16. Due to the inductive character ofthe stator winding 16, the waveform of current lac lags behind thewaveform of voltage Vac. V1 indicates a waveform of voltage between twoterminals of the first zener diode Z1, V2 indicates a waveform ofvoltage between two terminals of the second zener diode Z2, Vdcindicates a waveform of voltage between two output terminals C and D ofthe AC-DC conversion circuit 28, Ha indicates a waveform of a signaloutput by the output terminal H1 of the position sensor 20, and Hbindicates a rotor magnetic field detected by the position sensor 20. Inthis embodiment, in a case that the position sensor 20 is powerednormally, the output terminal H1 outputs a logic high level in a casethat the detected rotor magnetic field is North, or the output terminalH1 outputs a logic low level in a case that the detected rotor magneticfield is South.

In a case that the rotor magnetic field Hb detected by the positionsensor 20 is North, in a first positive half cycle of the AC powersupply, the supply voltage is gradually increased from a time instant t0to a time instant t1, the output terminal H1 of the position sensor 20outputs a high level, and a current flows through the resistor R1, theresistor R3, the diode D5 and the control electrode G and the secondanode T2 of the TRIAC 26 sequentially. The TRIAC 26 is switched on in acase that a drive current flowing through the control electrode G andthe second anode T2 is greater than a gate triggering current Ig. Oncethe TRIAC 26 is switched on, the two nodes A and B are shorted, acurrent flowing through the stator winding 16 in the motor is graduallyincreased until a large forward current flows through the stator winding16 to drive the rotor 14 to rotate clockwise as shown in FIG. 3. Sincethe two nodes A and B are shorted, there is no current flowing throughthe AC-DC conversion circuit 28 from the time instant t1 to a timeinstant t2. Hence, the resistors R1 and R2 do not consume electricenergy, and the output of the position sensor 20 is stopped due to nopower is supplied. Since the current flowing through two anodes T1 andT2 of the TRIAC 26 is large enough (which is greater than a holdingcurrent Ihold), the TRIAC 26 is kept to be switched on in a case thatthere is no drive current flowing through the control electrode G andthe second anode T2. In a negative half cycle of the AC power supply,after a time instant t3, a current flowing through T1 and T2 is lessthan the holding current Ihold, the TRIAC 26 is switched off, a currentbegins to flow through the AC-DC conversion circuit 28, and the outputterminal H1 of the position sensor 20 outputs a high level again. Sincea potential at the point C is lower than a potential at the point E,there is no drive current flowing through the control electrode G andthe second anode T2 of the TRIAC 26, and the TRIAC 26 is kept to beswitched off. Since the resistance of the resistors R1 and R2 in theAC-DC conversion circuit 28 are far greater than the resistance of thestator winding 16 in the motor, a current currently flowing through thestator winding 16 is far less than the current flowing through thestator winding 16 from the time instant t1 to the time instant t2 andgenerates very small driving force for the rotor 14. Hence, the rotor 14continues to rotate clockwise due to inertia. In a second positive halfcycle of the AC power supply, similar to the first positive half cycle,a current flows through the resistor R1, the resistor R3, the diode D5,and the control electrode G and the second anode T2 of the TRIAC 26sequentially. The TRIAC 26 is switched on again, and the current flowingthrough the stator winding 16 continues to drive the rotor 14 to rotateclockwise. Similarly, the resistors R1 and R2 do not consume electricenergy since the two nodes A and B are shorted. In the next negativehalf cycle of the power supply, the current flowing through the twoanodes T1 and T2 of the TRIAC 26 is less than the holding current Ihold,the TRIAC 26 is switched off again, and the rotor continues to rotateclockwise due to the effect of inertia.

At a time instant t4, the rotor magnetic field Hb detected by theposition sensor 20 changes to be South from North, the AC power supplyis still in the positive half cycle and the TRIAC 26 is switched on, thetwo nodes A and B are shorted, and there is no current flowing throughthe AC-DC conversion circuit 28. After the AC power supply enters thenegative half cycle, the current flowing through the two anodes T1 andT2 of the TRIAC 26 is gradually decreased, and the TRIAC 26 is switchedoff at a time instant t5. Then the current flows through the secondanode T2 and the control electrode G of the TRIAC 26, the diode D6, theresistor R4, the position sensor 20, the resistor R2 and the statorwinding 16 sequentially. As the drive current is gradually increased,the TRIAC 26 is switched on again at a time instant t6, the two nodes Aand B are shorted again, the resistors R1 and R2 do not consume electricenergy, and the output of the position sensor 20 is stopped due to nopower is supplied. There is a larger reverse current flowing through thestator winding 16, and the rotor 14 continues to be driven clockwisesince the rotor magnetic field is South. From the time instant t5 to thetime instant t6, the first zener diode Z1 and the second zener diode Z2are switched on, hence, there is a voltage output between the two outputterminals C and D of the AC-DC conversion circuit 28. At a time instantt7, the AC power supply enters the positive half cycle again, the TRIAC26 is switched off when the current flowing through the TRIAC 26 crosseszero, and then a voltage of the control circuit is gradually increased.As the voltage is gradually increased, a current begins to flow throughthe AC-DC conversion circuit 28, the output terminal H1 of the positionsensor 20 outputs a low level, there is no drive current flowing throughthe control electrode G and the second anode T2 of the TRIAC 26, hence,the TRIAC 26 is switched off. Since the current flowing through thestator winding 16 is very small, nearly no driving force is generatedfor the rotor 14. At a time instant t8, the power supply is in thepositive half cycle, the position sensor outputs a low level, the TRIAC26 is kept to be switched off after the current crosses zero, and therotor continues to rotate clockwise due to inertia. According to anembodiment of the present invention, the rotor may be accelerated to besynchronized with the stator after rotating only one circle after thestator winding is energized.

In the embodiment of the present invention, by taking advantage of afeature of a TRIAC that the TRIAC is kept to be switched on althoughthere is no drive current flowing though the TRIAC once the TRIAC isswitched on, it is avoided that a resistor in the AC-DC conversioncircuit still consumes electric energy after the TRIAC is switched on,hence, the utilization efficiency of electric energy can be improvedsignificantly.

FIG. 7 shows a circuit diagram of a drive circuit 42 for a synchronousmotor according to an embodiment of the present disclosure. The statorwinding 16 of the synchronous motor is connected in series with the ACpower supply 24 between the two nodes A and B. A first anode T1 of theTRIAC 26 is connected to the node A, and a second anode T2 of the TRIAC26 is connected to the node B. The AC-DC conversion circuit 28 isconnected in parallel with the TRIAC 26 between the two nodes A and B.An AC between the two nodes A and B is converted by the AC-DC conversioncircuit 28 into a low voltage DC, preferably, a low voltage ranging from3V to 18V. The AC-DC conversion circuit 28 includes a first resistor R1and a full wave bridge rectifier connected in series between the twonodes A and B. The full wave bridge rectifier includes two rectifierbranches connected in parallel, one of the two rectifier branchesincludes a first diode D1 and a third diode D3 reversely connected inseries, and the other of the two rectifier branches includes a secondzener diode Z2 and a fourth zener diode Z4 reversely connected inseries, the high voltage output terminal C of the AC-DC conversioncircuit 28 is formed at a connection point of a cathode of the firstdiode D1 and a cathode of the third diode D3, and the low voltage outputterminal D of the AC-DC conversion circuit 28 is formed at a connectionpoint of an anode of the second zener diode Z2 and an anode of thefourth zener diode Z4. The output terminal C is connected to a positivepower supply terminal of the position sensor 20, and the output terminalD is connected to a negative power supply terminal of the positionsensor 20. The switch control circuit 30 includes a third resistor R3, afourth resistor R4, and a fifth diode D5 and a sixth diode D6 reverselyconnected in series between the output terminal H1 of the positionsensor 20 and the control electrode G of the controllable bidirectionalAC switch 26. A cathode of the fifth diode D5 is connected to the outputterminal H1 of the position sensor, and a cathode of the sixth diode D6is connected to the control electrode G of the controllablebidirectional AC switch. One terminal of the third resistor R3 isconnected to the high voltage output terminal C of the AC-DC conversioncircuit, and the other terminal of the third resistor R3 is connected toa connection point of an anode of the fifth diode D5 and an anode of thesixth diode D6. Two terminals of the fourth resistor R4 are connected toa cathode of the fifth diode D5 and a cathode of the sixth diode D6respectively.

FIG. 8 shows a circuit diagram of a drive circuit 44 for a synchronousmotor according to a further embodiment of the present invention. Thedrive circuit 44 is similar to the drive circuit 42 in the previousembodiment and, the drive circuit 44 differs from the drive circuit 42in that, the zener diodes Z2 and Z4 in the drive circuit 42 are replacedby general diodes D2 and D4 in the rectifier of the drive circuit 44. Inaddition, a zener diode Z7 is connected between the two output terminalsC and D of the AC-DC conversion circuit 28 in the drive circuit 44.

FIG. 9 shows a circuit diagram of a drive circuit 46 for a synchronousmotor according to further embodiment of the present invention. Thestator winding 16 of the synchronous motor is connected in series withthe AC power supply 24 between the two nodes A and B. A first anode T1of the TRIAC 26 is connected to the node A, and a second anode T2 of theTRIAC 26 is connected to the node B. The AC-DC conversion circuit 28 isconnected in parallel with the TRIAC 26 between the two nodes A and B.An AC voltage between the two nodes A and B is converted by the AC-DCconversion circuit 28 into a low voltage DC, preferably, a low voltageranging from 3V to 18V. The AC-DC conversion circuit 28 includes a firstresistor R1 and a full wave bridge rectifier connected in series betweenthe two nodes A and B. The full wave bridge rectifier includes tworectifier branches connected in parallel, one of the two rectifierbranches includes two silicon control rectifiers S1 and S3 reverselyconnected in series, and the other of the two rectifier branchesincludes a second diode D2 and a fourth diode D4 reversely connected inseries. The high voltage output terminal C of the AC-DC conversioncircuit 28 is formed at a connection point of a cathode of the siliconcontrol rectifier S1 and a cathode of the silicon control rectifier S3,and the low voltage output terminal D of the AC-DC conversion circuit 28is formed at a connection point of an anode of the second diode D2 andan anode of the fourth diode D4. The output terminal C is connected to apositive power supply terminal of the position sensor 20, and the outputterminal D is connected to a negative power supply terminal of theposition sensor 20. The switch control circuit 30 includes a thirdresistor R3, an NPN transistor T6, and a fourth resistor R4 and a fifthdiode D5 connected in series between the output terminal H1 of theposition sensor 20 and the control electrode G of the controllablebidirectional AC switch 26. A cathode of the fifth diode D5 is connectedto the output terminal H1 of the position sensor. One terminal of thethird resistor R3 is connected to the high voltage output terminal C ofthe AC-DC conversion circuit, and the other terminal of the thirdresistor R3 is connected to the output terminal H1 of the positionsensor. A base of the NPN transistor T6 is connected to the outputterminal H1 of the position sensor, an emitter of the NPN transistor T6is connected to an anode of the fifth diode D5, and a collector of theNPN transistor T6 is connected to the high voltage output terminal C ofthe AC-DC conversion circuit.

In this embodiment, a reference voltage may be input to the cathodes ofthe two silicon control rectifiers S1 and S3 via a terminal SC1, and acontrol signal may be input to control terminals of S1 and S3 via aterminal SC2. The rectifiers S1 and S3 are switched on in a case thatthe control signal input from the terminal SC2 is a high level, or areswitched off in a case that the control signal input from the terminalSC2 is a low level. Based on the configuration, the rectifiers S1 and S3may be switched between a switch-on state and a switch-off state in apreset way by inputting the high level from the terminal SC2 in a casethat the drive circuit operates normally. The rectifiers S1 and S3 areswitched off by changing the control signal input from the terminal SC2from the high level to the low level in a case that the drive circuitfails. In this case, the TRIAC 26, the conversion circuit 28 and theposition sensor 20 are switched off, to ensure the whole circuit to bein a zero-power state.

FIG. 10 shows a circuit diagram of a drive circuit 48 for a synchronousmotor according to another embodiment of the present invention. Thedrive circuit 48 is similar to the drive circuit 46 in the previousembodiment and, the drive circuit 48 differs from the drive circuit 46in that, the silicon control diodes S1 and S3 in the drive circuit 46are replaced by general diodes D1 and D3 in the rectifier of the drivecircuit 48, and a zener diode Z7 is connected between the two terminalsC and D of the AC-DC conversion circuit 28. In addition, in the drivecircuit 48 according to the embodiment, a preset steering circuit 50 isdisposed between the switch control circuit 30 and the TRIAC 26. Thepreset steering circuit 50 includes a first jumper switch J1, a secondjumper J2 switch and an inverter NG connected in series with the secondjumper switch J2. Similar to the drive circuit 46, in this embodiment,the switch control circuit 30 includes the resistor R3, the resistor R4,the NPN transistor T5 and the diode D6. One terminal of the resistor R4is connected to a connection point of an emitter of the transistor T5and an anode of the diode D6, and the other terminal of the resistor R4is connected to one terminal of the first jumper switch J1, and theother terminal of the first jumper switch J1 is connected to the controlelectrode G of the TRIAC 26, and the second jumper switch J2 and theinverter NG connected in series are connected across two terminals ofthe first jumper switch J1. In this embodiment, when the first jumperswitch J1 is switched on and the second jumper switch J2 is switchedoff, similar to the above embodiments, the rotor 14 still startsclockwise; when the second jumper switch J2 is switched on and the firstjumper switch J1 is switched off, the rotor 14 starts counterclockwise.In this case, a starting direction of the rotor in the motor may beselected by selecting one of the two jumper switches to be switched onand the other to be switched off. Therefore, in a case that a drivingmotor is needed to be supplied for different applications havingopposite rotational directions, it is just needed to select one of thetwo jumper switches J1 and J2 to be switched on and the other to beswitched off, and no other changes need to be made to the drive circuit,hence, the drive circuit according to this embodiment has goodversatility.

As discussed above, the position sensor 20 is configured for detectingthe magnetic pole position of the permanent magnet rotor 14 of thesynchronous motor 10 and outputting a corresponding signal. The outputsignal from the position sensor 20 represents some characteristics ofthe magnetic pole position such as the polarity of the magnetic fieldassociated with the magnetic pole position of the permanent magnet rotor14 of the synchronous motor 10. The detected magnetic pole position isthen used, by the switch control circuit 30, control the controllablebidirectional AC switch 26 to be switched between a switch-on state anda switch-off state in a predetermined way, based on, together with themagnetic pole position of the permanent magnet rotor, the polarityinformation of the AC power supply 24 which may be obtained from theAC-DC conversion circuit 28.

More details are disclosed about a magnetic sensor that comprisesaspects of both the position sensor 20 and the switch control circuit30. In describing the details of the magnetic sensor related to both theposition sensor 20 and the switch control circuit 30, the presentteaching of this continuation-in-part application more focuses onvarious details related to the realization of the position sensor 20within the magnetic sensor as disclosed herein.

The magnetic sensor in the present teaching employs at least one foldedcascode amplifier. The folded cascode amplifier can efficiently amplifya very small input signals to have a great gain. In addition, the foldedcascode amplifier is configured with excellent frequency characteristicsand is capable of processing signals expanded in a very wide frequencyrange. Further, the magnetic sensor in the present teaching may bedirectly connected to the city AC power supply with no need ofadditional A/D converting equipment. Therefore, the present teachingfacilitates the implementation of the magnetic sensor into variousfields. Further, the magnetic field detecting circuit can effectivelyamply the detected magnetic field signal, regulate the voltage andfilter interference signals. Therefore, the magnetic sensor can generatemore accurate signal with respect to the polarity of the externalmagnetic field to control the operation of the electric rotor.

Additional novel features will be set forth in part in the descriptionwhich follows, and in part will become apparent to those skilled in theart upon examination of the following and the accompanying drawings ormay be learned by production or operation of the examples. The novelfeatures of the present teachings may be realized and attained bypractice or use of various aspects of the methodologies,instrumentalities and combinations set forth in the detailed examplesdiscussed below. The magnetic sensor, the signal processing methodimplemented in the magnetic sensor, and the motor using the magneticsensor and the signal processing method disclosed herein below can beachieved using any circuit technology known to one of ordinary skill inthe art including but not limited to the integrated circuit and othercircuit implementations.

FIG. 11 illustrates an exemplary schematic diagram of a magnetic sensor,according to an embodiment of the present teaching. The magnetic sensoraccording to this embodiment comprises an input port 1102, a magneticfield detecting circuit 1104 and an output port 1106. Input port 1102 isconfigured to connect to an external power supply and provide power tomagnetic field detecting circuit 1104. In some embodiments, the externalpower supply is a direct current (DC) power supply. In anotherembodiment, the external power supply is an alternative current (AC)power supply. Magnetic field detecting circuit 1104 is configured todetect an external magnetic field and generate a magnetic fielddetecting signal. The magnetic field detecting signal 1106 is thenapplied to control the operating status of the magnetic sensor and themotor or any electric equipment that uses the magnetic sensor.

Magnetic field detecting circuit 1104 may comprise a magnetic sensingelement 1108, a signal processing element 1110, and a conversion element1114. Magnetic sensing element 1108 is configured to sense the externalmagnetic field and output a first detecting signal 1120. First detectingsignal 1120 outputted from magnetic sensing element 1108 includes atleast a magnetic field signal and a deviation signal. The magnetic fieldsignal indicates an actual magnetic voltage signal associated with theexternal magnetic field that is sensed by magnetic sensing element 1108.The deviation signal is a bias signal inherited in magnetic sensingelement 1108.

As the actual magnetic voltage signal may be interfered by at least theinherited bias signal, signal processing element 1110 is configured toamplify the received first detecting signal 1120, remove theinterference signals from first detecting signal 1120, and generate asecond detecting signal 1122. In some embodiments, signal processingelement 1110 may comprise at least one folded cascode amplifier 1112.

The conversion element 1114 is configured to convert second detectingsignal 1122 into magnetic field detecting signal and output magneticfield detecting signal via output port 1106. In some embodiments,magnetic field detecting signal is a switching detecting signal.

FIG. 12 illustrates an exemplary schematic diagram of the signalprocessing element 1110, according to an embodiment of the presentteaching. Signal processing element 1110 according to FIG. 11 comprisesa first chopper switch (Z1) 1202 and a first chopper amplifier (IA)1204. First chopper switch 1202 is configured to separate the deviationsignal and the magnetic field signal which will be carried on a basebandfrequency and a chopper frequency, respectively. First chopper amplifier1204 is configured to amplify the deviation signal and the magneticfield signal and switch the amplified deviation signal and the magneticfield signal to the chopper frequency and the baseband frequency,respectively, for transmission. In some embodiments, the chopperfrequency is greater than 100K Hz, and the baseband frequency is lessthan 200 Hz.

In some embodiments, when the external power supply is an AC powersupply, the baseband frequency is proportional to the frequency of theAC power supply. In some embodiments, the baseband frequency is twicethe frequency of the AC power supply.

In some embodiments, signal processing element 1110 may further comprisea low-pass filter (LPF) 1206 configured to remove the deviation signaltransmitted via the chopper frequency.

In this embodiments, each of the inputs and outputs of first chopperswitch (Z1) 1202, first chopper amplifier (IA) 1204 and low-pass filter(LPF) 1206 are illustrated in a single line. It should be appreciatedthat FIG. 12 is for illustrative purpose. The present teaching is notintended to be limiting. Each of the inputs and outputs of first chopperswitch (Z1) 1202, first chopper amplifier (IA) 1204 and low-pass filter(LPF) 1206 may be one or more input/output signals. In some embodiments,each of the inputs and outputs of first chopper switch (Z1) 1202, firstchopper amplifier (IA) 1204 and low-pass filter (LPF) 1206 include oneor more pairs of differential signals.

FIG. 13A illustrates an exemplary schematic diagram of a chopperamplifier 1204, according to an embodiment of the present teaching.First chopper amplifier (IA) 1204 in FIG. 12 comprises a first amplifier(A1) 1302 and a second chopper switch (Z2) 1304. First amplifier (A1)1302 is configured to perform a first stage amplification of thedeviation signal and the magnetic field signal from first chopper switch(Z1) 1202. In some embodiments, first amplifier (A1) 1302 is implementedusing the at least one folded cascode amplifier such as 1112. Secondchopper switch (Z2) 1304 is configured to switch the amplified deviationsignal and the magnetic field signal to the chopper frequency and thebaseband frequency for transmission, respectively.

FIG. 13B illustrates an exemplary schematic diagram of a chopperamplifier 1204, according to another embodiment of the present teaching.According to the illustrated embodiment, first chopper amplifier (IA)1204 in FIG. 12 may comprise a second amplifier (A2) 1306 in addition tofirst amplifier (A1) 1302 and second chopper switch (Z2) 1304. Secondamplifier (A2) 1306 is configured to further perform a second stageamplification of the deviation signal and the magnetic field signal fromsecond chopper switch (Z2) 1304. In some embodiments, second chopperswitch (Z2) 1304 is implemented based on a single-stage amplifier.

It should be appreciated that the connections of first amplifier (A1)1302, second chopper switch (Z2) 1304 and second amplifier (A2) 1306 inFIG. 13B are for illustrative purpose. The present teaching is notintended to be limiting. In some embodiments, second amplifier (A2) 1306may be disposed between first amplifier (A1) 1302 and second chopperswitch (Z2) 1304.

FIG. 14 illustrates an exemplary schematic diagram of a magnetic sensor,according to another embodiment of the present teaching. The magneticsensor according to the illustrate embodiment comprises an input port1408, a rectifier circuit 1402, a magnetic field detecting circuit 1404,output control circuit 1406, and an output port 1410. Input port 1408 inthis embodiment comprises a pair of input ports 1408A and 1408B thatconnect to the external power supply. In some embodiments, input port1408 may connect to the external power supply serial. In yet otherembodiments, input port 1408 may connect to the external power supply inparallel.

Rectifier circuit 1402 may be implemented based on a full wave rectifierbridge and a voltage regulator (not shown). A full wave rectifier bridgemay be configured to convert an AC signal from the AC power supply intoa DC signal. A voltage regulator may be configured to regulate the DCsignal within a pre-set range. Rectifier circuit 1402 supplies theregulated DC signal to magnetic field detecting circuit 1404 and outputcontrol circuit 1406.

In this illustrated embodiment, magnetic field detecting circuit 1404comprises a Hall detector 1420, a first chopper switch 1422, a firstchopper amplifier 1424, a sample-and-hold circuit 1426, a filter circuit1428, and a comparator circuit 1430. Hall detector 1420 connects torectifier circuit 1402 to detect magnetic field signal and output thedetected magnetic field signal to first chopper switch 1422. Firstchopper switch 1422 is configured to perform the same functions as firstchopper switch 1202 shown in FIG. 12. First chopper switch 1422 outputsa first pair of differential signal {P1, N1} to first chopper amplifier1424.

First chopper amplifier 1424 may be implemented based on what isillustrated in FIG. 13B. Thus, first chopper amplifier 1424 comprises afirst amplifier (A1) 1302, a second chopper switch (Z2) 1304, and asecond amplifier (A2) 1306. First amplifier (A1) 1302 performs the firststage amplification of the received first pair of differential signal{P1, N1}. Second chopper switch (Z2) 1304 is configured to directlyoutput the amplified differential signal {P1, N1} in a first half of aclock cycle, and switch the amplified differential signal {P1, N1} tooutput in a second half of the clock cycle. Second chopper switch (Z2)1304 outputs a second pair of differential signal {P2, N2}. The secondpair of differential signal {P2, N2} may be further amplified by secondamplifier (A2) 1306 before outputted to sample-and-hold circuit 1426.

Sample-and-hold circuit 1426 is configured to sample the amplifiedsecond pair of differential signal {P2, N2} outputted from first chopperamplifier 1424 in FIG. 14 during the first half and the second half ofthe clock cycle, respectively. Outputs of sample-and-hold circuit 1426comprise two pairs of differential signals {P2A, N2A} and {P2B, N2B},where the pair of {P2A, N2A} is outputted during the first half of theclock cycle and the pair of {P2B, N2B} is outputted during the secondhalf of the clock cycle.

Filter circuit 1428 is configured to remove the deviation signal fromthe two pairs of differential signals {P2A, N2A} and {P2B, N2B}, andamplify of the differential signals {P2A, N2A} and {P2B, N2B}, andoutput a third differential signals {P3, N3} to comparator circuit 1430.

Comparator circuit 1430 is configured to compare the third pair ofdifferential signals {P3, N3} with a pair of reference voltage signals,and determine the polarity of the external magnetic field based on thecomparison results. Comparator circuit 1430 generates a magnetic fielddetecting signal indicating the determined polarity of the externalmagnetic field and outputs the same to output control circuit 1406. Insome embodiments, the magnetic field detecting signal is a switchingmagnetic field detecting signal.

Output control circuit 1406 is configured to control the magnetic sensorto operate in a state in response to the determined polarity of theexternal magnetic field. The magnetic sensor may operate in a pluralityof states. For example, a first state may correspond to a scenario inwhich a load current flows from inside to outside of the magnetic sensorvia the output port 1410, and a second state may correspond to ascenario in which a load current flows from outside to inside themagnetic sensor via output port 1410. In some embodiments, the magneticsensor may operate in a third status in which, no current flows throughoutput port 1410.

The actual magnetic voltage signal is normally very small. For example,it is commonly to be less than 1 millivolt. However, the deviationsignal generated by Hall detector 1420 is often higher, say, nearly 10millivolt. The present teaching aims to remove the deviation signal andamplifies the actual magnetic voltage signal so that the actual magneticvoltage signal at an operable level can be provided to an motor or anyelectric equipment that uses the magnetic sensor. In some embodiments,the voltage supply to magnetic field detecting circuit 1404 is at thelevel of about 2.5V. When the detected signal outputted by Hall detector1420 passes through first chopper switch 1422, first chopper amplifier1424, sample-and-hold circuit 1426, and filter circuit 1428, thedetected signal may be amplified 1000 to 2000 times of the originalpower gain, preferably somewhere in-between such as 1600 times theoriginal power gain. As a result, the detected actual magnetic voltagesignal is amplified to be approximately half of the voltage levelsupplied to magnetic field detecting circuit 1404. In some embodiments,the first chopper amplifier 1424 is configured to achieve a gain greaterthan that of filter circuit 1428. For example, the gain achieved byfirst chopper amplifier 1424 may be 50 while the gain achieved by filtercircuit 1428 is 32.

FIG. 15 illustrates an exemplary schematic diagram of a rectifiercircuit 1402, according to an embodiment of the present teaching.According to the embodiment illustrated in FIG. 15, a full waverectifier bridge is employed to implement the rectifier circuit 1402,which comprises a first diode 1502, a second diode 1504, a third diode1506, and a fourth diode 1508; and a voltage regulator comprises aregulator diode 1520. First diode 1502 and second diode 1504 areconnected in serial. Third diode 1506 and fourth diode 1508 are alsoconnected in serial. The cathode of first diode 1502 and the anode ofsecond diode 1504 are configured to connect to input port 1408A, whichsupplies voltage VAC+. The cathode of third diode 1506 and the anode offourth diode 1508 are configured to connect to input port 1408B, whichsupplies voltage VAC−. The anode of regulator diode 1502 is configuredto connect to the anode of first diode 1502 and the third diode 1506,which is further connected to ground. The cathode of regulator diode1520 is connects to the cathode of second diode 1504 and fourth diode1508 connecting together to voltage VDD.

FIG. 16 illustrates an exemplary circuit diagram of a Hall detector 1420and the first chopper switch, according to an embodiment of the presentteaching. According to the illustrated embodiment, Hall detector 1420and first chopper switch 1422 are integrated as a single circuit in FIG.16. Hall detector 1420 comprises a Hall detecting circuit board withfour connecting ports 1602, 1604, 1606, and 1608. Connecting ports 1602and 1606 are disposed opposing each other and connecting ports 1604 and1608 are disposed opposing each other. First chopper switch 1422comprises four switches 1610, 1612, 1614, and 1616. Switch 1610 controlsconnecting ports 1602 and 1608 to alternately connect to power supplyVCC, and switch 1612 controls connecting ports 1604 and 1606 toalternately connect to ground. Switch 1614 controls connecting ports1602 and 1608 to alternately output differential signal P1, and switch1616 controls connecting ports 1604 and 1606 to alternately outputdifferential signal N1. In some embodiments, Hall detector 1420 andfirst chopper switch 1422 are configured such that when one ofconnecting ports 1602 and 1608 connects to power supply VCC, the otherone of connecting ports 1602 and 1608 outputs differential signal P1.Meanwhile, when one of connecting ports 1604 and 1606 connects to theground, the other one of connecting ports 1604 and 1606 outputsdifferential signal N1. For example, when connecting port 1602 connectsto power supply VCC and connecting port 1606 connects to the ground,connecting ports 1608 and 1604 output the pair of differential signal{P1, N1}. In the alternative, when connecting port 1608 connects topower supply VCC and connecting port 1604 connects to the ground,connecting ports 1602 and 1606 output the first pair of differentialsignal {P1, N1}.

In some embodiments, power supply VCC may be a constant voltage sourceachieved via performing voltage dropping and regulating on the output ofrectifier circuit 1402. In other embodiments, power supply VCC may be aconstant current source.

In some embodiments, each of switches 1610, 1612, 1614, and 1616comprises a pair of switches configured to be high-voltage conduction orlow-voltage conduction. Each of such pairs of switches may be controlledby a pair of complementary clock signals. By supplying two pairs ofcomplementary clock signals in the same frequency to switches 1610,1612, 1614, and 1616, respectively, Hall detector 1420 and first chopperswitch 1422 can generate the first pair differential signals {P1, N1}.

FIG. 17 illustrates exemplary signal outputs, according to the circuitdiagram of FIG. 16. Signal CK1 denotes a clock signal. Signal Vosdenotes the deviation signal that is inherited in Hall detector 1420. Ingeneral, signal Vos depends on the physical characteristics of Halldetector 1420. Vin and −Vin denote the actual magnetic field voltagesignal outputted by first chopper switch 1422 during the first half andthe second half of clock signal CK1, respectively. The actual magneticfield voltage signal is an ideal magnetic field voltage signalassociated with the external magnetic field without the interferencecaused by the deviation signal. During the first half and the secondhalf of clock signal CK1, the actual magnetic field voltage signalsoutputted by first chopper switch 1422 have the same amplitude andopposite polarity. Vout denotes the output of first chopper switch 1422,which is the actual magnetic field voltage signal Vin or −Vinsuperimposed by or in combination with deviation signal Vos. Firstchopper switch 1422 separates the actual magnetic field voltage signalVin or Vin and deviation signal Vos, and switches them onto a chopperfrequency and a baseband frequency, respectively. In some embodiments,the chopper frequency is the frequency of clock signal CK1 and thebaseband frequency is the polarity changing frequency of the externalmagnetic field.

FIG. 18 illustrates an exemplary circuit diagram of filter circuit 1428,according to an embodiment of the present teaching. Filter circuit 1428as illustrated in FIG. 14 may comprise a first filter (F1) 1802 and asecond filter (F2) 1804. First filter (F1) 1802 is configured to apply afirst stage addition to each of two pairs of signals {P2A, P2B} and{N2A, N2B} that are outputted from sample-and-hold circuit 1426, It isto remove the deviation signals. First filter (F1) 1802 may be furtherconfigured to perform a first stage gain amplifying on the signals afterthe first stage addition processing. Second filter (F2) 1804 isconfigured to apply a second stage addition and/or a second stage gainamplifying on the output signals from first filter (F1) 1802 andgenerate the third pair of differential signals {P3, N3}. The gain offirst filter (F1) 1802 may be configured to be smaller than the gain ofsecond filter (F2) 1804. For example, the gain of first filter (F1) 1802is 4 and the gain of second filter (F2) 1804 is 8.

It should be appreciated that the diagram of the filter circuit 1428described above is for illustrative purpose. The present teaching is notintended to be limiting. Filter circuit 1428 may comprise more or lessfilters than what is illustrated in FIG. 18. In some embodiments, filtercircuit 1428 may comprise only one filter. However, in this situation,the only filter may have to be configured with a large resistance inorder to achieve a better gain.

FIG. 19 illustrates an exemplary circuit diagram of comparator circuit1430, according to an embodiment of the present teaching. Comparatorcircuit 1430 of FIG. 14 may perform the same function as A/D conversionelement 1114 of FIG. 11. In this embodiment, comparator circuit 1430 maybe a delay comparator including a first comparator (C1) 1902, a secondcomparator (C2) 1904, and a latch logic circuit (S) 1906. The input tofirst comparator (C1) 1902 includes the third pair of differentialsignals {P3, N3} and a pair of reference voltage signals {Vh, V1}, whereVh is a high voltage signal and V1 is a low voltage signal. The input tosecond comparator (C2) 1904 includes the same pairs of signals that areinput to first comparator (C1) 1902 except that the pair of referencevoltage signals {Vh, V1} is connected in opposite polarities. Firstcomparator (C1) 1902 is configured to compute an output voltage V1 fromfilter 1408, wherein V1=P3−N3, and a high voltage threshold Rh, whereinRh=Vh−V1. First comparator (C1) 1902 compares the output voltage V1 withthe high voltage threshold Rh. When V1>Rh, first comparator (C1) 1902outputs high and when V1<Rh, first comparator (C1) 1902 outputs low.Second comparator (C2) 1904 is configured to compare output voltage V1from filter 1408 with a low voltage threshold R1, wherein R1=V1−Vh. WhenV1>R1, second comparator (C2) 1904 outputs high and when V1<R1, secondcomparator (C2) 1904 outputs low. As Rh is greater than R1, when V1>Rh,which means that V1>R1, both first comparator (C1) 1902 and secondcomparator (C2) 1904 output high. When V1<R1, which means that V1<Rh,both first comparator (C1) 1902 and second comparator (C2) 1904 outputlow. When RV>V1<Rh, first comparator (C1) 1902 outputs low and secondcomparator (C2) 1904 outputs high. The comparison results from firstcomparator (C1) 1902 and second comparator (C2) 1904 are sent to latchlogic circuit (S) 1906. Latch logic circuit (S) 1906 is configured togenerate a voltage signal based on the comparison results. The voltagesignal is further sent to output control circuit 1406 to control theoperation status of the magnetic sensor. Details on how latch logiccircuit (S) 1906 generates a voltage signal based on the comparisonresults are described below.

FIG. 20 illustrates an exemplary schematic diagram for determining thepolarity of the magnetic field, according to an embodiment of thepresent teaching. When latch logic circuit (S) 1906 receives thecomparison results from first comparator (C1) 1902 and second comparator(C2) 1904, which indicate that the output voltage of filter circuit 1428V1 is greater than Rh, latch logic circuit (S) 1906 generates a firstsignal indicating a change to sink current state. When latch logiccircuit (S) 1906 receives the comparison results from first comparator(C1) 1902 and second comparator (C2) 1904, which indicate that theoutput voltage of filter circuit 1428 is less than R1, latch logiccircuit (S) 1906 generates a second signal indicating a change to sourcecurrent state. When latch logic circuit (S) 1906 receives the comparisonresults from first comparator (C1) 1902 and second comparator (C2) 1904,which indicate that the output voltage of filter circuit 1428 V1satisfies R1<V1<Rh, latch logic circuit (S) 1906 generates a thirdsignal indicating no change to the state. In some embodiments, the firstvoltage indicates that the external magnetic field exhibits a firstpolarity, and the second voltage indicates that the external magneticfield exhibits a second polarity.

FIG. 20 illustrates that in some embodiments, when the magnetic fieldstrength of the external magnetic field reaches a working point Bop,comparator circuit 1430 generates the first signal, while when themagnetic field strength of the external magnetic field is below areleasing point Brp, comparator circuit 1430 generates the secondsignal. When the magnetic field strength of the external magnetic fieldis between the working point Bop and the releasing point Brp, comparatorcircuit 1430 remains the current output without change.

FIG. 21 illustrates exemplary signal outputs in a clock cycle, accordingto an embodiment of the present teaching. As shown in FIG. 21 (A), thefirst pair of differential signals {P1, N1} is the output of firstchopper switch 1422, the second pair of differential signals {P2, N2} isthe output of first chopper amplifier 1424, and the third pair ofdifferential signals {P3, N3} is the output of filter circuit 1428.{P1A, N1A} is a pair of differential signals outputted from firstchopper switch 1422 during the first half of the clock cycle, and {P1B,N1B} is a pair of differential signals outputted from first chopperswitch 1422 during the second half of the clock cycle. {P2A, N2A} is apair of differential signals outputted from first chopper amplifier 1424during the first half of the clock cycle, and {P2B, N2B} is a pair ofdifferential signals outputted from first chopper amplifier 1424 duringthe second half of the clock cycle.

As described above, Vout denotes the output of first chopper switch1422, which is the actual magnetic field voltage signal Vin or −Vinsuperimposed by deviation signal Vos. In another aspect, Vout denotesthe difference between the first pair of differential signals {P1, N1},where P1 and N1 have the same amplitude and opposite polarity.Therefore, P1A, P1B, N1A, and N1B are denoted by the followingequations:

$\begin{matrix}\begin{Bmatrix}{{P\; 1A} = \frac{{Vos} + {Vin}}{2}} \\{{P\; 1B} = \frac{{Vos} - {Vin}}{2}} \\{{N\; 1A} = {{{- P}\; 1A} = {- \frac{{Vos} + {Vin}}{2}}}} \\{{N\; 1B} = {{{- P}\; 1B} = {- \frac{{Vos} - {Vin}}{2}}}}\end{Bmatrix} & (1)\end{matrix}$

When first chopper amplifier 1424 in FIG. 14 implements the embodimentillustrated in FIG. 13B, first chopper amplifier 1424 comprises a firstamplifier (A1) 1302, a second chopper switch (Z2) 1304, and a secondamplifier (A2) 1306. The first pair of differential signals {P1, N1} isamplified to differential signals {P1′, N1′} after passing through firstamplifier (A1) 1302. {P1′, N1′} and their respective components duringthe first half and the second half of the clock cycle are denoted by thefollowing equations:

$\begin{matrix}\begin{Bmatrix}{{P\; 1A^{\prime}} = {A\frac{{Voff} + {Vin}}{2}}} \\{{P\; 1B^{\prime}} = {A\frac{{Voff} - {Vin}}{2}}} \\{{N\; 1A^{\prime}} = {{{- P}\; 1A^{\prime}} = {{- A}\frac{{Voff} + {Vin}}{2}}}} \\{{N\; 1B^{\prime}} = {{{- P}\; 1B^{\prime}} = {{- A}\frac{{Voff} - {Vin}}{2}}}}\end{Bmatrix} & (2)\end{matrix}$

A denotes the amplifying gain of first amplifier (A1) 1302. Voff denotesthe deviation signal outputted by first amplifier (A1) 1302, whichincludes the deviation signal generated by Hall detector 1420 Vos andthe deviation signal generated by first amplifier (A1) 1302. Forillustrative purpose, coefficients A and ½ are ignored from thedescription herein below.

As second chopper switch (Z2) 1304 directly outputs the amplifieddifferential signal {P1, N1} on the first half of a clock cycle, andswitchingly outputs the amplified differential signal {P1, N1} on thesecond half of the clock cycle, the outputs from second chopper switch(Z2) 1304 comprise two components at each half of the clock cycle. Afterpassing through sample-and-hold circuit 1426, the four components {P2A,P2B, N2A, N2B} denoted by the following equations are inputted to filtercircuit 1428.

$\begin{matrix}\begin{Bmatrix}{{P\; 2A} = {{P\; 1A^{\prime}} = {{Voff} + {Vin}}}} \\{{P\; 2B} = {{N\; 1B^{\prime}} = {- \left( {{Voff} - {Vin}} \right)}}} \\{{N\; 2A} = {{N\; 1A^{\prime}} = {- \left( {{Voff} + {Vin}} \right)}}} \\{{N\; 2B} = {{P\; 1B^{\prime}} = {{Voff} - {Vin}}}}\end{Bmatrix} & (3)\end{matrix}$

Further, the third pair of differential signals {P3, N3} outputted byfilter circuit 1428 are denoted by the following equations:

$\begin{matrix}\begin{Bmatrix}{{P\; 3} = {{{P\; 2A} + {P\; 2B}} = {{\left( {{Voff} + {Vin}} \right) - \left( {{Voff} - {Vin}} \right)} = {2{Vin}}}}} \\{{N\; 3} = {{{N\; 2A} + {N\; 2B}} = {{{- \left( {{Voff} + {Vin}} \right)} + \left( {{Voff} - {Vin}} \right)} = {{- 2}{Vin}}}}}\end{Bmatrix} & (4)\end{matrix}$

As shown in the above equations, the deviation signals in the third pairof differential signals {P3, N3} are removed by filter circuit 1428. Thethird pair of differential signals {P3, N3} thus, comprises only theactual magnetic field voltage signal.

FIG. 21 (B) shows that after the first chopper switch (e.g., 1202 inFIG. 12), the actual magnetic field voltage signal Vin and the deviationsignal Voff are separated to a chopper frequency of 400 kHz and abaseband frequency of 100 Hz, respectively, where the chopper frequencyis the frequency of the clock signal. After the second chopper switch(e.g., 1304 in FIG. 13A, 13B), the actual magnetic field voltage signalVin and the deviation signal Voff are switched to the baseband frequencyand the chopper frequency, respectively. Then after the filter circuit(e.g., 1206 in FIG. 12), the deviation signal Voff is filtered out. Whenthe magnetic sensor is implemented to control a synchronous motor, theexternal magnetic field may be a permanent magnetic motor field inwhich, the polarity changing frequency is twice the AC power sourcefrequency. If the synchronous motor is provided with the city AC powersupply of 50 Hz or 60 Hz, the baseband frequency is 100 Hz or 120 Hz.After passing through multiple chopper switches and amplifiers, theactual magnetic field voltage signal and the deviation signal areseparated in a very wide frequency range. As such, chopper amplifierimplemented in the present teaching is configured to accommodate thevery wide frequency range.

FIG. 22 illustrates an exemplary circuit diagram of the output controlcircuit 1406, according to an embodiment of the present teaching. Outputcontrol circuit 1406 according to the illustrated embodiment comprises afirst switch 2202 and a second switch 2204. First switch 2202 is coupledwith output port 1410 to form a first current path, and second switch2204 is coupled with output port 1410 to form a second current path. Theelectric current flows through the first and the second current paths inopposite directions. First switch 2202 and second switch 2204 arecontrolled by magnetic detecting signal to be selectively connected. Insome embodiments, first switch 2202 is a transistor, and second switch2204 is either a diode or a transistor.

In some embodiments, first switch 2202 is configured as low-voltage passand second switch 2204 is configured as high-voltage pass. The controlends of both first switch 2202 and second switch 2204 are connected tothe output of magnetic detecting circuit 1404. The output of firstswitch 2202 and the input of the second switch 2204 are both connectedto output port 1410. The input of first switch 2202 may be connected toa high-voltage end 2206, for example, a DC power source or the outputVDD from rectifier circuit 1402, and the output of second switch 2204may be connected to a low-voltage end 2208, for example, a ground. Ifthe output of magnetic detecting circuit 1404 is a low voltage signal,first switch 2202 is connected and second switch 2204 is disconnected.Consequently, a load current flows into first switch 2202 fromhigh-voltage end 2206 and flows out via output port 1410. If the outputof magnetic detecting circuit 1404 is a high voltage signal, secondswitch 2204 is connected and first switch 2202 is disconnected.Consequently, a load current flows into second switch 2204 from outputport 1410 and flows out via low-voltage end 2208.

FIG. 23 illustrates an exemplary circuit diagram of the output controlcircuit, according to another embodiment of the present teaching. Outputcontrol circuit 1406 according to the illustrated embodiment comprisesfirst switch 2302 and second switch 2304. First switch 2302 isconfigured as be high-voltage pass, and second switch 2304 is configuredto be a one-way diode. The control end of first switch 2302 and thecathode of second switch 2304 are both connected to the output ofmagnetic detecting circuit 1404. In some embodiments, the control end offirst switch 2302 is connected to the output of magnetic detectingcircuit 1404 via a resistance 2308. The input of first switch 2302 maybe connected to the output of rectifier circuit 1402 (referring to FIG.14). The output of first switch 2302 and the anode of the second switchare both connected to output port 1410. Similar to the embodimentillustrated in FIG. 22, first switch 2302 is coupled with output port1410 to form a first current path, and second switch 2304 is coupledwith output port 1410 to form a second current path. The electriccurrent flows through the first and the second current paths in oppositedirections. If the output of magnetic detecting circuit 1404 is a highvoltage signal, first switch 2302 is connected and second switch 2304 isdisconnected. Consequently, a load current flows into first switch 2302from high-voltage end 2306 and flows out via output port 1410. If theoutput of magnetic detecting circuit 1404 is a low voltage signal,second switch 2304 is connected and first switch 2302 is disconnected.Consequently, a load current flows into second switch 2304 from outputport 1410.

FIG. 24 illustrates an exemplary circuit diagram of the output controlcircuit, according to yet another embodiment of the present teaching.Output control circuit 1406 according to the illustrated embodimentcomprises a one-way switch 2402 and a resistance 2404. One-way switch2402 is connected between magnetic field detecting circuit 1404 andoutput port 1410 to form a first current path, and resistance 2404 isconnected between magnetic field detecting circuit 1404 and output port1410 to form a second current path, where the electric current flowsthrough the first and the second current paths in opposite directions.If the output of magnetic detecting circuit 1404 is a high voltagesignal, one-way switch 2402 is connected and a load current flowsthrough one-way switch 2402 from the output of magnetic field detectingcircuit 1404 to output port 1410. If the output of magnetic detectingcircuit 1404 is a low voltage signal, one-way switch 2402 isdisconnected and a load current flows through resistance 2404 fromoutput port 1410 to the output of magnetic field detecting circuit 1404.

The magnetic sensor in the present teaching may be directly connected tothe city AC power supply with no need of additional A/D convertingequipment. Therefore, the present teaching facilitates theimplementation of the magnetic sensor into various fields. Further, themagnetic field detecting circuit can effectively amply the detectedmagnetic field signal, regulate the voltage and filter interferencesignals. Therefore, the magnetic sensor can generate more accuratesignal with respect to the polarity of the external magnetic field tocontrol the operation of the electric rotor.

FIG. 25 illustrates an exemplary schematic diagram of a motor 2500 whichincorporates a magnetic sensor constructed in accordance with thepresent teaching. The motor may comprise an AC power supply 2502, amotor 2504, a magnetic sensor 2508, and a bidirectional switch 2510. Insome embodiments, the motor 2500 may further comprise a voltage droppingcircuit 2506 configured to reduce the level of AC power supply 2502before providing to magnetic sensor 2508. The output Pout of Magneticsensor 2508 is electrically connected to a control end of bidirectionalswitch 2510.

In some embodiments, magnetic sensor 2508 is configured to output adriving current to bidirectional switch 2510 when AC power supply 2502operates at a positive half cycle and when magnetic field detectingcircuit 1404 in magnetic sensor 2508 determines that the externalmagnetic field exhibits a first polarity. In the alternative, outputcontrol circuit 1406 in magnetic sensor 2508 is configured to controlmagnetic sensor 2508 to output a driving current to bidirectional switch2510 when AC power supply 2502 operates at a negative half cycle andmagnetic field detecting circuit 1404 therein determines that theexternal magnetic field exhibits a second polarity opposite to the firstpolarity. Output control circuit 1406 in magnetic sensor 2508 is furtherconfigured to control magnetic sensor 2508 not to output a drivingcurrent to bidirectional switch 2510 when AC power supply 2502 operatesat a negative half cycle and magnetic field detecting circuit 1404therein determines that the external magnetic field exhibits a firstpolarity, or when AC power supply 2502 operates at a positive half cycleand magnetic field detecting circuit 1404 determines that the externalmagnetic field exhibits a second polarity.

In the embodiments where magnetic sensor 2508 uses a rectifier circuitas illustrated in FIG. 15 and an output control circuit as illustratedin FIG. 22, the input of first switch 2202 of FIG. 22 is configured toconnect to the voltage output VDD of bridge full waver rectifier of FIG.15, and the output of second switch 2204 is configured to connect toground. When AC power supply 2502 operates at a positive half cycle andmagnetic field detecting circuit 1404 outputs a low voltage, firstswitch 2202 is connected and second switch is disconnected, an electriccurrent flows in a direction passing through AC power supply 2502, motor2504, VAC+, magnetic sensor 2508, and bidirectional switch 2510. Withinmagnetic sensor 2508, the electric current flows through the voltageoutput of bridge full waver rectifier and first switch 2202. In someembodiments, the electric current flows through voltage dropping circuit2506 before magnetic sensor 2508. When AC power supply 2502 operates ata negative half cycle and magnetic field detecting circuit 1404 outputsa high voltage, first switch 2202 is disconnected and second switch isconnected, an electric current flows in an opposite direction passingthrough AC power supply 2502, bidirectional switch 2510, magnetic sensor2508, and motor 2504. Within magnetic sensor 2508, the electric currentflows through second switch 2204, ground output of bridge full waverrectifier, first diode 1502 and VAC+. When AC power supply 2502 operatesat a positive half cycle and magnetic field detecting circuit 1404outputs a high voltage, or when AC power supply 2502 operates at anegative half cycle and magnetic field detecting circuit 1404 outputs alow voltage, first switch 2202 and second switch 2204 are bothdisconnected. Consequently, there is no driving current flowing throughPout of magnetic sensor 2508.

FIG. 26 illustrates an exemplary schematic diagram of a synchronousmotor 2600 which incorporates a magnetic sensor constructed inaccordance with the present teaching. Synchronous motor 2600 comprises astator and a rotor 2602 configured to rotate relative to the stator. Thestator comprises a stator core 2604 and a stator coil 2612 configured towind around stator core 2604. Stator core 2604 may be made of any softmagnetic materials such as iron, cast iron, electrical steel, silicon,etc. Rotor 2602 is configured to rotate at a constant speed of 60 f/p(i.e., revolutions per minute, rpm) when connecting to an AC powersupply in serial, where f is the frequency of the AC power supply and pis number of pole pairs in rotor 2602.

Stator core 2604 is configured with a pair of opposing pole portions2608A and 2608B. Each of the pair of opposing pole portions (2608A,2608B) has a pole arc surface, for example, 2610A and 2610B. The surfaceof rotor 2602 opposes the pole arc surfaces (2610A, 2610B) and forms anair gap 2606 in between. In some embodiments, the air gap 2606 betweenrotor 2602 and the stator is mostly even with very little uneven gaparea. In some embodiments, each of pole surfaces (2610A, 2610B) isfurther configured with a starting groove, for example, 2614. Pole arcsurfaces (2610A, 2610B) are concentric with rotor 2602 except the areaof starting grooves. The configuration of starting grooves forms anuneven magnetic field internally. Further, the configuration of startinggrooves ensure that when rotor 2602 is static, a polar S1 of rotor 2602is tilted to an angle relative to a central polar S2 of pole portions2608A and 2608B. Such configuration allows the rotor 2602 to have astarting torque each time the motor is turned on. In this embodiment,polar S1 of rotor 2602 is a separation boundary between two magneticpoles of rotor 2602, and central polar S2 passes through the opposingpole portions 2608A and 2608B in the center. The stator and rotor 2602are both configured with two magnetic poles.

Output control circuit 1406 according to the present teaching controlsbidirectional switch 2510 to switch the status between connecting anddisconnecting based on the polarity of AC power supply 2502 and thepolarity of the external magnetic field, and further controls thepower-up status of stator coil 2612. As such, the magnetic fieldgenerated by the stator can coordinate with the magnetic field positionof rotor 2602 to drive the rotor to rotate in one single direction, andtherefore, ensures the motor to have a constant rotating direction eachtime the motor is powered up.

It should be appreciated that the examples described above are forillustrative purpose. The present teaching is not intended to belimiting. The stator and rotor 2602 may be configured with differentmagnetic poles, such as four or six magnetic poles. In addition, thestator and rotor 2602 may have different magnetic poles with respect toeach other.

Those skilled in the art will recognize that the present teachings areamenable to a variety of modifications and/or enhancements. For example,although the implementation of various components described above may beembodied in a hardware device, it can also be implemented as a softwareonly solution—e.g., an installation on an existing server. In addition,the units of the host and the client nodes as disclosed herein can beimplemented as a firmware, firmware/software combination,firmware/hardware combination, or a hardware/firmware/softwarecombination.

While the foregoing has described what are considered to be the bestmode and/or other examples, it is understood that various modificationsmay be made therein and that the subject matter disclosed herein may beimplemented in various forms and examples, and that the teachings may beapplied in numerous applications, only some of which have been describedherein. It is intended by the following claims to claim any and allapplications, modifications and variations that fall within the truescope of the present teachings.

We claim:
 1. A magnetic sensor, comprising: an input port to beconnected to an external power supply; a magnetic field detectingcircuit configured to generate a magnet detection signal; an outputcontrol circuit configured to control operation of the magnetic sensorin response to the magnet detection signal; and an output port, whereinthe magnetic field detecting circuit includes: a magnetic sensingelement configured to detect an external magnetic field and output adetection signal, a signal processing element configured to amplify thedetection signal and removing interference from the detection signal togenerate processed detection signal, and a conversion element configuredto convert the processed detection signal into the magnet detectionsignal, which is used to control the magnetic sensor to operate in atleast one of a first state and a second state responsive to at least themagnet detection signal, wherein in the first state, a load currentflows from the output port to outside of the magnetic sensor, and in thesecond state, a load current flows from the outside into the output portof the magnetic sensor, wherein the signal processing element comprisesa folded cascode amplifier.
 2. The magnetic sensor of claim 1, whereinthe detection signal includes a magnetic field signal and a deviationsignal, and the signal processing element comprises: a first chopperswitch configured to separate the detection signal into the deviationsignal and the magnetic field signal corresponding to a chopperfrequency and a baseband frequency, respectively, a chopper amplifierconfigured to amplify the deviation signal and the magnetic field signaland to switch the amplified deviation signal and the amplified magneticfield signal onto the chopper frequency and the baseband frequency,respectively, and a filter circuit configured to filter out thedeviation signal at the chopper frequency.
 3. The magnetic sensor ofclaim 2, wherein the chopper amplifier comprises a first amplifier; anda second chopper switch, wherein the first amplifier includes the foldedcascode amplifier that is configured to perform first-stageamplification on the deviation signal and the magnetic field signal fromthe first chopper switch to generate the amplified deviation signal andthe amplified magnetic field signal, respectively, and the secondchopper switch is configured to switch the amplified deviation signaland the amplified magnetic field signal onto the chopper frequency andthe baseband frequency, respectively.
 4. The magnetic sensor of claim 2,wherein the chopper frequency is greater than 100 K Hertz and thebaseband frequency is less than 200 Hertz.
 5. The magnetic sensor ofclaim 3, wherein the chopper amplifier further comprises a secondamplifier connected in serial to the second chopper switch, wherein thesecond amplifier is configured to perform second-stage amplification onthe amplified deviation signal switched onto the chopper frequency andthe amplified magnetic field signal switched onto the basebandfrequency.
 6. The magnetic sensor of claim 2, wherein the signalprocessing element further comprises a sample-and-hold circuit coupledbetween the chopper amplifier and the filter circuit, wherein thesample-and-hold circuit is configured to sample a first pair ofdifferential signals during a first half and a second half of a clockcycle, respectively and output two pairs of sampled differential signalsduring the clock cycle.
 7. The magnetic sensor of claim 6, wherein thefilter circuit further comprises a first filter configured to compute asecond pair of differential signals based on the two pairs of sampleddifferential signals.
 8. The magnetic sensor of claim 7, wherein thefilter circuit further comprises a second filter configured to furtheramplify the second pair of differential signals, remove the deviationsignal, and generate a third pair of differential signals.
 9. Themagnetic sensor of claim 1, further comprising: a rectifying circuitcoupled with the input port and configured to provide a voltage supplyto the magnetic field detection circuit.
 10. The magnetic sensor ofclaim 1, wherein the external power supply is an alternating current(AC) power supply, and the magnet detection signal is a switchingdetection signal, wherein a switching frequency of the magneticdetection signal is proportional to a frequency of the AC power supplyor is twice the frequency of the AC power supply.
 11. The magneticsensor of claim 1, further comprising: an output control circuitconfigured to control the magnetic sensor to operate in at least one ofthe first state and the second state based on the magnet detectionsignal, wherein the output control circuit comprises: a first switchcoupled with the output port to form a first current path allowing theload current flows from the output port to outside of the magneticsensor in the first state; and a second switch coupled with the outputport to form a second current path allowing the load current flows fromoutside of the magnetic sensor to the output port in the second state,wherein the first and second switches operate based on the magnetdetection signal to selectively turn on the first and second currentpaths.
 12. The magnetic sensor of claim 11, wherein the first switch isa diode and the second switch is either a diode or a transistor.
 13. Anintegrated circuit for a magnetic sensor, comprising: an input port tobe connected to an external power supply; an output port; and a magneticfield detecting circuit configured to generate a magnet detection signaland comprising: a magnetic sensing element configured to detect anexternal magnetic field and output a detection signal, wherein thedetection signal includes a magnetic field signal and a deviationsignal, a signal processing element configured to amplify the detectionsignal and remove interference to generate a processed detection signal,and a conversion element configured to convert the processed detectionsignal to the magnet detection signal, which is used to control themagnetic sensor to operate in at least one of a first state and a secondstate responsive to at least the magnet detection signal, wherein thesignal processing element comprises a first chopper switch configured toseparate the detection signal into a magnetic field signal and adeviation signal corresponding to a chopper frequency and a basebandfrequency, respectively; a chopper amplifier configured to separatelyamplify the magnetic field signal and the deviation signal and switchthe amplified deviation signal and the amplified magnetic field signalonto the chopper frequency and the baseband frequency, respectively, anda filter circuit configured to remove the deviation signal that has beenswitched to the chopper frequency, wherein the signal processing elementcomprises a folded cascode amplifier.
 14. The integrated circuit for amagnetic sensor of claim 13, further comprising a rectifying circuitcoupled with the input port, wherein the rectifying circuit providesvoltage supply to the magnetic field detection circuit.
 15. Theintegrated circuit for a magnetic sensor of claim 13, wherein thechopper amplifier comprises: a first amplifier; and a second chopperswitch, wherein the first amplifier includes the folded cascodeamplifier that is configured to perform first-stage amplification on thedeviation signal and the magnetic field signal from the first chopperswitch to generate the amplified deviation signal and the amplifiedmagnetic field signal, respectively, and the second chopper switch isconfigured to switch the amplified deviation signal and the amplifiedmagnetic field signal onto the chopper frequency and the basebandfrequency, respectively.
 16. The integrated circuit for a magneticsensor of claim 15, wherein the chopper amplifier further comprises asecond amplifier connected in serial to the second chopper switch,wherein the second amplifier is configured to perform second-stageamplification on the amplified deviation signal switched onto thechopper frequency and the amplified magnetic field signal switched ontothe baseband frequency.
 17. The integrated circuit for a magnetic sensorof claim 13, wherein the external power supply is an alternating current(AC) power supply, and the magnet detection signal is a switchingdetection signal, wherein a switching frequency of the magneticdetection signal is proportional to a frequency of the AC power supplyor is twice the frequency of the AC power supply.
 18. The integratedcircuit for a magnetic sensor of claim 16, further comprising: an outputcontrol circuit configured to control the magnetic sensor to operate inat least one of the first state and the second state based on the magnetdetection signal, wherein the output control circuit comprises: a firstswitch coupled with the output port to form a first current pathallowing the load current flows from the output port to outside of themagnetic sensor in the first state; and a second switch coupled with theoutput port to form a second current path allowing the load currentflows from outside of the magnetic sensor to the output port in thesecond state, wherein the first and second switches operate based on themagnet detection signal to selectively turn on the first and secondcurrent paths.
 19. A motor assembly comprising: a motor coupled with anexternal power supply that provides alternating current (AC) power tothe motor; a magnetic sensor configured to detect a magnetic fieldgenerated by the motor; and a bidirectional switch configured to controlthe motor based on an operating state of the magnetic sensor determinedbased on the detected magnetic field, wherein the magnetic sensorcomprises: a magnetic field detecting circuit configured to detect themagnetic field and generate a magnet detection signal based on thedetected magnetic field, and comprises: a magnetic sensing elementconfigured to detect an external magnetic field and output a detectionsignal, a signal processing element configured to amplify the detectionsignal and removing interference from the detection signal to generateprocessed detection signal, and a conversion element configured toconvert the processed detection signal into the magnet detection signal,which is used to control the magnetic sensor to operate in at least oneof a first state and a second state responsive to at least the magnetdetection signal; and an output control circuit configured to control,based on the magnet detection signal, the magnetic sensor to operate inat least one of a first state and a second state responsive to at leastthe magnet detection signal, wherein in the first state, current flowsfrom outside of the magnetic sensor into the magnetic sensor, and in thesecond state, the current flows from the magnetic sensor to the outsideof the magnetic sensor, wherein the signal processing element comprisesa folded cascode amplifier.
 20. The motor of claim 19, wherein the motorcomprises a stator and a rotor, wherein the bidirectional switch isconfigured to control a conductive state of the stator in response tothe first state and the second state, respectively, such that the statoroperates in a manner consistent with a magnetic position of the rotorrelative to the stator to drive the rotor in order to rotate in apre-determined direction.